The feature of bagease that likely is the problem is that it does not present a "surface". Lidar mapping has this problem when surveying over a vegetated area. They solve the problem by having a large enough spot to return a sort of average, and then filtering for first return (vegetation) and last return (ground). See the attachment for a discussion.
Since this is essentially a post processing filter, performed by in this case the sensor firmware, there is a possibility that some provider of conveyor volume sensors has attempted a solution of this problem. Look for one that can do a volume measurement of agricultural products like loose straw and silage.